This L-shaped, tubular airlock was added to Endeavour’s Payload Bay in 1997. Prior to this, an airlock existed internally in the Mid-deck of the Crew Module between the toilet and a bank of computers and storage lockers. An external airlock allowed not only more area in the cramped Mid-deck but also access both out into the Payload Bay for spacewalks and up, vertically, to connect with the International Space Station.

This airlock has been removed from Endeavour and will not be displayed at the California Science Center. Instead, it’ll likely be incorporated into a future spacecraft.